Characterization of Low Load Ethanol Dual-Fuel Combustion using Single and Split Diesel Injections on a Heavy-Duty Engine

The use of two different fuels to control the in-cylinder charge reactivity of compression ignition engines has been shown as an effective way to achieve low levels of nitrogen oxides (NOx) and soot emissions. The port fuel injection of ethanol on a common rail, direct injected diesel engine increases this reactivity gradient. The objective of this study is to experimentally characterize the controllability, performance, and emissions of ethanol-diesel dual-fuel combustion in a single cylinder heavy-duty engine. Three different diesel injection strategies were investigated: a late split, an early split, and an early single injection. The experiments were performed at low load, where the fuel conversion efficiency is typically reduced due to incomplete combustion. Ethanol substitution ratios varied from 44-80% on an energy input basis. The results reveal that a less premixed charge promoted by late split diesel injections allowed for more direct control over the combustion phasing at the expense of higher NOx and soot emissions. Early split injections resulted in a more homogeneous charge, yielding low overall emissions and low pressure rise rates. The early single injection strategy resulted in high indicated efficiency and similar emissions to early split injections at higher ethanol percentages. The highest indicated efficiency was obtained at an ethanol substitution ratio of 65%. Higher combustion inefficiencies and NOx emissions were generally observed as the ethanol fraction increased.